The present invention relates to a refractometer for measuring the index of refraction of a sample medium by measuring the transmission of light through a sensor, which transmission is a substantially linear function of the index of refraction.
Known refractometers normally serve the purpose of measuring the index of refraction of a fluid. Refractometers of the type under discussion have been known in the art and have been disclosed, for example in the German Pat. No. 2,137,842 or U.S. Pat. No. 3,282,149. Inasmuch as the index of refraction of the sample medium depends upon the temperature a so-called reference sensor for eliminating the temperature influence has been employed, which has been surrounded with the reference medium. The outlet value of the reference sensor with the known refractive index is inversely proportional to the temperature of the sample medium or of the environment. The temperature influence can be eliminated from the output value of the sample medium sensor in the test data processing device and is normalized relative to the temperature in the indicator device. That is, the refractive index of the sample medium referred to the ambient temperature is indicated on the indicator.
In known refractometers the sample medium sensor and the reference medium sensor are separated from each other for measuring the index of refraction of a fluid. The sensors are arranged in two separate vessels having the same temperature; the vessels are respectively filled with the probe for the reference medium and the probe for the sample medium. Such a refractometer is bulky, and is unsuitable or difficult in handling and for a mobile use.